The following present disclosure is provided in relation to Proton Exchange Membrane (PEM) fuel cell stacks. The method of manufacture may also be used for other types of fuel cell stacks such as SOFC fuel cell stacks, Molten Carbonate Fuel Cells (MCFC) or Direct Methanol Fuel Cells (DMFC). Further, the present disclosure can also be used for electrolysis cells such as Solid Oxide Electrolysis Cells and such cell stacks. The electro-chemical reactions and the function of a fuel cell or an electrolysis cell is not the essence of the present invention, thus this will not be explained in detail, but considered known for a person skilled in the art.
In a traditional fuel cell stack 114 (as shown in FIG. 1A), a plurality of fuel cell units 118 and traditional flat end plates 110 are assembled to form a stack 114. It is understood that a UEA 116 may be disposed onto a bipolar plate thereby forming a fuel cell 118 among the other similarly constructed fuel cells 118 additional fuel cells are schematically represented by phantom lines 115. The UEA 116 may include diffusion mediums (also known as a gas diffusion layer) disposed adjacent to an anode face and a cathode face of a membrane electrolyte assembly (MEA). The MEA includes a thin proton-conductive, polymeric, membrane-electrolyte having an anode electrode film formed on one face thereof, and a cathode electrode film formed on the opposite face thereof. In general, such membrane-electrolytes are made from ion-exchange resins, and typically comprise a perfluoronated sulfonic acid polymer such as NAFION™ available from the E.I. DuPont de Nemeours & Co. The anode and cathode films, on the other hand, typically comprise (1) finely divided carbon particles, very finely divided catalytic particles supported on the internal and external surfaces of the carbon particles, and proton conductive material (e.g., NAFION™) intermingled with the catalytic and carbon particles, or (2) catalytic particles, sans carbon, dispersed throughout a polytetrafluoroethylene (PTFE) binder.
The efficiency of the fuel cell stack 114 is dependent on small contact resistance between the various UEA's 116 and bipolar plates. This compression forces 132 must be large enough and evenly distributed throughout the length 130 of the fuel cell stack 114 to ensure electrical contact between each fuel cell 118, but not so significant such that excessive compression forces 132 damage the electrolyte, the electrodes, the electrical interconnect or impedes the gas flow over the UEA's 116. The compression of the fuel cell stack 114 is also vital for the seal between the layers of the stack to keep the stack gas tight. However, it is rather common to find varying compression forces 132 along the length 130 of the fuel cell stack 114 resulting in inefficient fuel cell stack 114 operation.
Under this scenario, excessively high compression forces 132 may occur at certain regions within a stack 114 while inadequate compression forces 132 may occur at other regions within the same stack. As indicated, unevenness across the stack can lead to damage or reduced performance of the fuel cell stack. Accordingly, there is a need to provide a method to manufacture a robust fuel cell stack which evenly distributes the loads (compression forces 132) along the length of the fuel cell stack from one end plate to the other end plate.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. Accordingly, there is a need for an improved end plate unit for a fuel cell stack which better distributes compression loads across the fuel cell stack.